Diffusion furnace loader

ABSTRACT

A furnace-loading mechanism for use with a diffusion furnace, the components thereof facilitating the entry and withdrawal of a wafer-bearing quartz boat member relative to a furnace through an articulated chain link construction which is capable of storage in a horizontal plane on the loader.

United States Patent [191 Redan 51 March 6, 1973 DIFFUSION FURNACELOADER [75] Inventor: Joseph Redan, P arsippany, NJ.

[73] Assignee: Simmonds Precision Products, Inc.,

Tarrytown, N.Y.

[22] Filed: July 28, 1971 [21] Appl. No.: 166,731

[52] U.S. Cl. ..2l4/34, 254/DlG. 6, 263/6 R [51] Int. Cl ..F27b 9/26[58] Field of Search...2l4/23, 26, 34, 18 R; 263/6 R;

254/DIG. 6; 219/1069, 10.71

[56] References Cited UNITED STATES PATENTS 3,563,434 2/1 97 1"siiav'g'r t i. .I ..214/23x 1/1971 Amerio ..2l4/34X 12/1966 Cloutier..2l4/l8R Primary Examiner-Robert G. Sheridan Att0rneyEdwin E. Greigg [57 ABSTRACT A furnace-loading mechanism for use with a diffusion furnace,the components thereof facilitating the entry and withdrawal of awafer-bearing quartz boat member relative to a furnace through anarticulated chain link construction which is capable of storage in ahorizontal plane on the loader.

9 Claims, 5 Drawing Figures PAIENIEM; 6 ma 7 4 29 1 "sum 30F 3 iW/ENTC-YJOSEPH REDAN DIFFUSION FURNACE LOADER This invention relates to animproved furnace loading mechanism to more expeditiously achievecompletely automatically the function of positioning a batch ofsemiconductor wafers into the fumace temperatur e flat zone and thewithdrawal at a controlled rate at the completion of the diffusionprocess.

Basically, the process consists of heating the semiconductor to bediffused to a high temperature in a furnace containing the vapors of theimpurity to be diffused into the semiconductor.

BACKGROUND OF THE INVENTION Transistor technology is now well known asthe fundamental of transistor construction. In 1948 Bell Laboratoriescreated the point contact transistor and principally because it provedto be unstable, it tended to oscillate.

Progress of this earlier type of transistor led to the development ofthe grown junction transistor which began with the melt of purifiedmaterial into which a seed or what is known as a small single crystal ofthe semiconductor material, was lowered. Later because the grownjunction transistor had a number of serious deficiencies, the alloyjunction transistor, with germanium as the semiconductor, came intoexistence and has proved to be a very successful design. However,continued experimentation developed the fact the silicon was moresuitable for high-powered semiconductors than germaniunnthe principalreason being that it could be used at much higher temperatures and,moreover, because processing techniques yielded more economical devices.As a natural consequence of the development of the semiconductordevices, there came into existence diffusion furnaces, this type offurnace having thermal energy which causes charge carriers, i.e.electrons and holes, to diffuse from one side at the p-n junction to theother side thereof. The law of diffusion states that the diffusionspecies will flow from the region of high concentration (the vapor) tothe region of low concentration (the semiconductor). I

To those skilled in this art it is well known that carefully preparedsemiconductor materials have a crystal structure which is called alattice. The outer or valence electrons of individual atoms are tightlybound to the electrons of adjacent atoms in electron-pair bonds. As aconsequence, in order to separate electron-pair bonds and provide freeelectrons for electrical conduction, one may add small amounts of otherelements having a different atomic structure to the semiconductor. It iswell known that these infinitesimal amounts of elements, calledimpurities, can be controlled and modified and that in order toaccomplish this, the resultant device, which is denoted as a wafer," ispositioned upon a quartz boat or carrier member, and thereafterintroduced into the diffusion furnace.

There are two types of diffusion-current furnaces, one type is open ateach end and the boat containing the wafers to be treated to changetheir atomic structure is transversed through the furnace on the boat onan endless chain, or the boat containing the wafers may be inserted intothe furnace by means of a quartz pedal which is manually operated by aworkman. The other type of furnace is open only at one end andheretofore it has been customary to insert the beater carrier memberbearing the wafers into thefurnace or retract it therefrom by theoperators quartz pedal.

OBJECTS AND ADVANTAGES OF THE INVENTION Accordingly, this inventionrelates to improvements in furnace loading devices, particularly for usewith diffusion furnaces.

Another object of the invention is to provide a selfcontained housingwhich includes all the necessary controls to fully automate thesubjection of the silicon wafers to the diffusion current of thefurnace.

Still another object of the invention is to provide the housing acircuitous trackway which acts as a guide means for a multiplicity ofarticulated link members which advance the wafer-bearing boat into andretract it from the furnace.

Yet another object of the invention is to provide a series ofinterconnected articulated link members which are adapted tobe actuatedby a power-driven sprocket member with the links being so designed as toalso form a means by which the wafer boat is moved into and out of thefurnace.

A still further object of the invention is to provide manually operablemeans for controlling the articulated link members and the wafer uponelectrical power failure.

These and other objects and advantages will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings. 7

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 discloses a side elevationalview of the furnace loader with a portion of the trackway extending intothe furnace;

FIG. 2 is a cross-sectional view on line 2-2 of FIG.

FIG. 3 is a top plan view of the furnace loaderand the wafer boat withthe drive elements for the boat shown schematically;

FIG. 4 is a cross-sectional view on line 4-4 of FIG. 2; and

FIG. 5 is a perspective view showing the drive chain, boat and trackwayin exploded form to better disclose their details.

DESCRIPTION OF THE EMBODIMENT Turning now to FIG. I, there is shown theleft side of the furnace loader housing 10 with its rear wall 11 securedto and in abutted relation with the front wall 12 of the diffusionfurnace 13, the entrance of which is denoted at 14.

There is also well shown in this particular view an enlarged aperture 15provided in the left side wall of the housing 10, this opening providingfor access not only to the knurled wheel 15a for manual drive of thesprocket wheel 16, all of which will be explained in greater detailhereinafter, but also for driving adjustment of the potentiometer, thenecessity for which will be apparent to those skilled in the art.

Referring at this time to FIG. 2 there is clearly shown therein thedrive motor 17, a gear reduction unit 18 associated therewith, and ashaft 19 extending therefrom, the terminus of which includes a minorpulley 20 securely fastened thereto in any suitable manner. Adjacentthereto and in driving relation with the minor pulley 20 through anendless belt means 21 is a major pulley 22.

A perpendicularly extending plurally apertured partition 23 includesmeans defining an opening denoted 24 and through which the shaft 25provided at one end with the pulley 22 and at its opposite end with theknurled drive means 15a is arranged to extend. As shown in FIG. 2, theshaft 25 includes a bearing means 26 for purposes that will be apparent.

Substantially medially of the partition 23 and the pulley 22 there issecured to the shaft 25, a gear member 27 which is provided with acollar means 28 and on which the sprocket member 16 is securelyarranged, as shown. It will be observed that the shaft 25 is sopositioned relative to an opening in the top wall (FIG. 4) of thecabinet that the teeth of the sprocket will extend up through thetrackway 31 and circumscribe an arcuate path therethrough and therebygain access to and drive the multiple chain link members 30 which areslidably confined on the trackway 31.

Referring at this time again to FIG. 1, there is generally denoted onthe front wall 32 of housing 10 several of the control members includingan on-and-off switch 33, a gauge for indicating the position of the boat34 relative to the furnace chamber 36 and one of several other switcheswhich, when operated by a skilled workman, will compensate for the rateof control of treatment of the wafers 35 carried by the boat 34, as wellas their preheat and dwell time within the furnace chamber.

The partition 23 (see FIGS. 1 and 4) is provided with an aperture 37which is covered by an arcuately slotted plate member 38, the slot 39thereof being arranged to receive a shaft 40, one end of which isaffixed to a plate element 41 pivoted as at 42 to the wall of thehousing with the opposite threaded end of the shaft 40 adapted toreceive a knurled knob 42a whereby the idler pulley 43 carried by plate41 can be swung in one direction to tension thebelt 21, and in theopposite direction for releasing tension thereon. In view of theforegoing, it will be apparent that by first loosening the knob 42relative to the shaft 40, whereupon the front wall of the knob (notshown) is disengaged from contact with plate 38, the pivotal plate 41can be moved to one side so the belt can be suitably tensioned and thenthe knob 42 once again turned down sufficiently in order that its frontwall will be brought into tight frictional engagement with the plate 38.v

It will be apparent that in the event of electrical power failure, suchas the well-known blackouts that have occurred extensively in recentyears on the East Coast of the United States, that the operator of thefurnace loader will be able to withdraw the boat 34 from the furnacechamber manually by merely loosening the knurled knob 42 and releasingthe tension from the drive belt so that the knob a carried at the end ofthe sprocket bearing shaft can be rotated to drive the sprocket in thedesired direction.

Turning now to FIG. 3 of the drawings, there is shown a top plateelement 44 which is securely fastened to' the housing 10 and is providedwith a guideway 45 having a reentrant bend portion 46 so that theinterconnected chain link members 30 can be fully retracted from thefurnace chamber in a horizontal plane and stored on the top of thehousing, as shown. The trackway 31 is securely mounted on the top wallof the housingand includes a terminal portion 47 that extendssubstantially the length of the furnace chamber 36. Thus, the chainlinks can be extended fully into the furnace (approximately 4 ft.) andentirely retracted therefrom so as to lie on the top of plate 44.

In FIG. 2 the rotary element 50 carried on shaft 51 and which is driventhrough gear means 52 that, in turn, is drivably associated with thesprocket is adapted to drive a shaft on which is mounted a contact armof a potentiometer, the position of the arm being arranged to determinethe resistance in the circuit with the latter elements enumerated notbeing illustrated.

Referring at this time to FIG. 4, there is shown a schematic view of theleft side wall of the housing 10 clearly illustrating the drivensprocket 16, the teeth of which are shown extending up through thetrackway and into engagement with the chain link members 30.

The exploded schematic view in FIG. 5 shows the quartz boat 34 whichincludes upright end walls 53-53 with lifting handles being shownextending therefrom, the latter facilitating positioning the boat on thelinks 30. The boat 34 can be provided with converging slid ing walls, asshown, or the wafer-receiving slotted surface may be merely concave, theboat member not forming any part of this invention. The lower surface ofthe boat 34 is provided with depressions (see FIG. 1) which receive theupstanding pins 54 of the interconnected chain links 30. e

SUMMARY TYPICAL OPERATING CYCLE A typical operating cycle consists ofthe operator preselecting one of two types of operating modes:

a. Run mode, which will drive the boat first to the dwell (if selected)and then to the diffusion zone.

b. Oscillate mode; selection of this mode of drive imposes anoscillation on the drive causing the boat to move plus or minus 2 inchesat both the dwell (if selected) and diffusion zone.

Step 1: Turn selector to set up position. Load boat Step 2: Select boatposition in furnace by turning selector potentiometer to positiondesired.

Step 3: Turn rate control to desired time one, two or three minutes forfull stroke. v

Step 4: Turn preheat dwell timer potentiometer to select length of timedesired.

Step 5: Turn preheat position potentiometer to select desired dwellposition in furnace.

Ref. At this time the operator has completed the set up and needs onlyturn selector knob to run mode.

Step 6: Turn selector to run mode.

That which is claimed is:

l. A furnace-loading mechanism comprising a laterally flexible andlongitudinally rigid, elongated means for moving a wafer-bearing boatmember for advancement into or retraction from the furnace and a supportmeans for said moving means, said support means comprising a housingcontaining a power driving means for the moving means, said supportmeans also including a guideway for the moving means, said guidewaybeing positioned in a horizontal plane on a top surface of said housing,said guideway first extending away from said furnace, curving laterallyand then extending towards said furnacefor compact storage of the movingmeans when retracted form the furnace and said guideway having anopening through which a portion of said driving means extends fordriving said moving means.

2. A furnace-loading mechanism as claimed in claim 1, wherein saiddriving means includes a control means adapted to advance thewafer-bearing boat to a preheat position within the furnace andthereafter automatically advance it to its dwell position therein.

3. A furnace-loading mechanism as claimed in claim 1, comprisingmanually operated means engaging said moving means for driving saidmoving means when the power means is not used.

4. A furnace-loading mechanism as claimed in claim 3, wherein both thepower drive and the manually operated means are drivingly connected to ameans for controlling the resistance of a potentiometer.

5. A furnace-loading mechanism as claimed in claim 1, wherein thedriving means includes a motor and a gear train between said motor andsaid moving means, and a movable idler means in the gear train forinterrupting power transmission between said motor and said movingmeans.

6. A furnace loading mechanism as claimed in claim 1, wherein theguideway has a portion extending into the furnace.

7. A furnace loading mechanism as claimed in claim 1, wherein saidmoving means includes articulated link members, a plurality of said linkmembers having means interengaging with means on said boat member.

8. A furnace-loading mechanism comprising a conveyor adapted to move awafer-bearing boat member for advancement into or retraction from thefurnace and a conveyor support means including a driving means for theconveyor, said conveyor support means also including a horizontallypositioned guideway for the conveyor having a reentrant bend for compactstorage of the conveyor when retracted from the furnace, said conveyorincluding articulated link members, each link member further including adetent means which is complemental to means carried by an adjacent linkmember, said detent means arranged to cooperate with means on said boatmember to advance the same into and retract it from the furnace.

9. A furnace-loading mechanism comprising a conveyor adapted to move awafer-bearing boat member for advancement into or retraction from thefurnace and a conveyor support means including a driving means for theconveyor, said conveyor support means also including a horizontallypositioned guideway for the conveyor having a reentrant bend for compactstorage of the conveyor when retracted from the furnace, said drivingmeans including an electricmotor drivingly connected to a sprocket meansfor driving said conveyor and a manually operated means also drivinglyconnected to said sprocket for driving the conveyor upon failure of themotor to operate.

i i 1! i

1. A furnace-loading mechanism comprising a laterally flexible andlongitudinally rigid, elongated means for moving a waferbearing boatmember for advancement into or retraction from the furnace and a supportmeans for said moving means, said support means comprising a housingcontaining a power driving means for the moving means, said supportmeans also including a guideway for the moving means, said guidewaybeing positioned in a horizontal plane on a top surface of said housing,said guideway first extending away from said furnace, curving laterallyand then extending towards said furnace for compact storage of themoving means when retracted form the furnace and said guideway having anopening through which a portion of said driving means extends fordriving said moving means.
 1. A furnace-loading mechanism comprising alaterally flexible and longitudinally rigid, elongated means for movinga wafer-bearing boat member for advancement into or retraction from thefurnace and a support means for said moving means, said support meanscomprising a housing containing a power driving means for the movingmeans, said support means also including a guideway for the movingmeans, said guideway being positioned in a horizontal plane on a topsurface of said housing, said guideway first extending away from saidfurnace, curving laterally and then extending towards said furnace forcompact storage of the moving means when retracted form the furnace andsaid guideway having an opening through which a portion of said drivingmeans extends for driving said moving means.
 2. A furnace-loadingmechanism as claimed in claim 1, wherein said driving means includes acontrol means adapted to advance the wafer-bearing boat to a preheatposition within the furnace and thereafter automatically advance it toits dwell position therein.
 3. A furnace-loading mechanism as claimed inclaim 1, comprising manually operated means engaging said moving meansfor driving said moving means when the power means is not used.
 4. Afurnace-loading mechanism as claimed in claim 3, wherein both the powerdrive and the manually operated means are drivingly connected to a meansfor controlling the resistance of a potentiometer.
 5. A furnace-loadingmechanism as claimed in claim 1, wherein the driving means includes amotor and a gear train between said motor and said moving means, and amovable idler means in the gear train for interrupting powertransmission between said motor and said moving means.
 6. A furnaceloading mechanism as claimed in claim 1, wherein the guideway has aportion extending into the furnace.
 7. A furnace loading mechanism asclaimed in claim 1, wherein said moving means includes articulated linkmembers, a plurality of said link members having means interengagingwith means on said boat member.
 8. A furnace-loading mechanismcomprising a conveyor adapted to move a wafer-bearing boat member foradvancement into or retraction from the furnace and a conveyor supportmeans including a driving means for the conveyor, said conveyor supportmeans also including a horizontally positioned guideway for the conveyorhaving a reentrant bend for compact storage of the conveyor whenretracted from the furnace, said conveyor including articulated linkmembers, each link member further including a detent means which iscomplemental to means carried by an adjacent link member, said detentmeans arranged to cooperate with means on said boat member to advancethe same into and retract it from the furnace.